This blog highlights how applications built around DWF can do more than what can be done just using paper. The blog covers the building (architectural/electrical/construction), manufacturing, and infrastructure (e.g., GIS, telecommunications) industries.

February 15, 2007

Autodesk Design Review 2008: DWF Version Compare Feature Overview

DWF Version Compare is one of the new features of Autodesk Design Review 2008. It is available from the Tools->Compare menu item. When invoked, the user is allowed to select a second DWF file and then a sheet from that file. The Compare capability then compares the current sheet to the selected sheet. Two markups are produced by this process:

Additions shows what geometry items would need to be added to the original sheet to make them appear the second sheet.

Deletions shows what geometry items would need to be removed from the original sheet because they do not appear on the second sheet

Differences are identified as additions and deletions. So if a piece of geometry changes, it shows up once as added and again as deleted. This may change in the future. Right now we don't have the data to determine that a piece of geometry in one DWF corresponds to the same piece of geometry in another DWF. Recall that DWF is a published format. It would be like trying to map graphics primitives to PEN UP/PEN DOWN commands in an HPGL file. We will fix that in the future. Doing so requires coordination with our design applications that publish DWF files.

The Additions and Deletions items are added to the currently open DWF file as regular markup items. Anything you can do with markup items (e.g., delete), you can do with these items. Think of the comparison tool as something that compares two sheets and creates the markups for you. It's as if you did this yourself but don't have to do so manually. As markups, you can save the resulting DWF file, print it, email it, etc. and they can see the results of the comparison. I can see the emails now: What do you mean nothing changed - look at this!

The Version Compare feature is based on an algorithm that interrogates the geometry that appears in the DWF file. Have the points that make up the geometry changed? For example: Is this line now longer or shorter?, Does the line have a different pattern?, or Has the shape of this polygon changed?.

As this is an initial implementation of Version Compare, it is important that users understand what Compare what it will and will not do.

Known Limitations

Version Compare is limited to 2D sheets. It does not evaluate 3D models. We already have a prototype of 3D comparison working. This will be coming in a future release.

Version Compare does not compare image data. Version Compare is currently based on geometry, not pixels. So it does not detect the color changes of the tiny dots that comprise photographs and other images that appear in DWF files. This too will be coming in a future release.

Version Compare detects changes in polyline attributes except color. In other words, detection includes changes for pattern, end style, join style, and weight. For example, if a solid line changes to a dashed line, Version Compare detects this difference. Similarly, Version Compare detects a thin line that changes to a wide line. Version Compare does not detect when nothing changes about a line except its color. In practice, patterns are used more frequently than color. For example, if a line changes from representing a gas line to a sewer line, even if the only thing that changes is the line pattern, and Version Compare detects this change.

Version Compare does not detect changes in polygon attributes for fill color and in some cases fill pattern. For example, if a filled area changes color from green to red, Version Compare will not detect it. This can happen in facilities management applications where color changes are associated with changes in office themeing. This limitation does not apply to hatch or gradient patterns. For example, Version Compare detects an area of a backyard that changes from GRASS to GRAVEL where the only change is the hatch pattern. This is because the hatch pattern for GRASS results in geometry in the DWF file that is different from the hatch pattern for GRAVEL.

Version Compare identifies everything on sheets as being different for comparisons of sheets that are published at different scales. In other words, if you compare two sheets published at different scales, you'll get lots of differences. In most instances, everything will show up as added and deleted. This happens because the numbers that represent the geometry in the DWF are all different when a different scale is used.

Version Compare identifies everything on the sheets as being different for comparisons of sheets that are published at DPI values. This is the same situation as with different scales.

Version Compare compares underlying geometry in a DWF file. If an original DWF file has a line from (0,0) to (2,2) and a subsequent DWF file has two lines from (0,0) to (1,1) and (1,1) to (2,2), Version Compare will detect this difference although the display appears identical in the Autodesk Design Review. This is an artifact of the DWF publishing process and will be investigated in conjunction with future development of DWF publishing applications.

The ability to identify what has changed from one version of a design to another is critical. Doing this electronically with a process that identifies additions and deletions goes beyond what can be done by aligning and eyeballing sheets of paper. This process will improve over time with future releases of Autodesk Design Review.